"Dithering: The introduction of digital noise by the DoD. The process by which the DoD used to add inaccuracy of GPS signals to promote Selective Availability".
They said it will not happen again. The ones who believe in this statement please raise their hands!
This is a real possibility any time they want the rest of the world to grind to a halt.
Even though Selective Availability only affect civilians, they are once again teaching Celestial. I got the message...
Even assuming the DOD would introduce error, the degree of that error when it was last introduced was on the order of 1/4 mile. If you are good enough with celestial nav to get your error down to +\- 1/4nm you shall now be hailed as a god amongst men.
On the other hand even if the US DOD did introduce this error all modern GPS chip sets ALSO pull from the EU geolocation sattelites. So the DOD would need to also convince the EU to participate. Modern chip sets ALSO pull from the Russian geolocation sattelites so they would need to be on board as well.
Frankly if there is a global conflict so large that the US, EU, and Russia all are involved and feel the need to step down GPS locations I doubt that exact positional accuracy will be your major problem.
In the next few years, China will also be launching its own sattelite location system, and chip sets will add them to the mix.
It is almost absurd to envision a global conflict of such a nature that every major world power is involved, and yet my biggest concern is GPS accuracy to +/- 1/4nm versus the 50' I get now.
Edit: apparently I missed a few... India is launching a local system that covers the area from the Suez Canal East to Japan, and Japan is launching its own system as well.
Right now all major chip manufacturers can operate on at least the us-GPS, and the Russian-GLOSNAS system, and most of them can operate on the Chinese and EU systems as well.
Celestial navigation as a practical matter is dead and buried. Other than the oldest US sattelites no other positioning system is even possible of selectively degrading their accuracy. And the new gen systems are designed to provide accuracy to +\- 1m or better, with the EU and Chinese system designed for +\- 1cm.